The invention relates generally to a continuous casting mold.
More particularly, the invention relates to a remotely adjustable continuous casting mold.
The continuous casting of large strands such as slabs is generally performed in a mold made up of two essentially parallel wide walls and two essentially parallel narrow walls which are located between the wide walls. The walls cooperate to define a casting passage of rectangular cross section.
The slab formed in a continuous casting mold constitutes a semifinished article which is subsequently rolled to produce plate. The width of the plate is a function of the width of the slab.
The production of plate by a mill is usually based on orders received by the mill. Frequently, the order log is such that casting of an entire slab having a single width would result in an excess of plate of a particular width. In such cases, it is desirable to change the width of the slab so as to produce plate of a different width.
Since it is difficult and uneconomical, if not impossible, to interrupt and then restart the casting of a slab in order to provide an opportunity for a width change, a mold which enables a width change to be effected while casting has been developed. This mold, which is known as a remotely adjustable mold, is designed in such a manner that the narrow walls may be moved towards and away from one another without stopping movement of the slab, i.e., without interrupting the casting operation.
The slab has a very thin skin when it initially forms in the mold. In order to avoid rupture of the skin during a width change, the narrow walls must be moved relatively slowly so that they constantly support the narrow faces of the slab. Therefore, it takes a certain amount of time to effect the width change. Since the slab continues moving while the width change takes place, the portion of the slab which passes through the mold during the period required to carry out the width change is tapered.
Due to the initial weakness of its skin, the slab must be supported even after it leaves the mold. To this end, a series of support zones is arranged downstream of the mold. Each support zone includes two essentially parallel wide sides made up of cooling grids, cooling plates or rollers which engage the wide faces of the slab. Each support zone further includes two essentially parallel narrow sides likewise made up of cooling grids, cooling plates or rollers which engage the narrow faces of the slab.
The first support zone following the mold is particularly critical since the skin of the slab has not had a chance to develop significantly and therefore requires substantial support. During normal operation, the four faces of the slab are in contact with the respective sides of the first support zone.
The narrow sides of the first support zone are movable towards and away from one another to allow for changes in the width of the slab. However, it is extremely difficult to synchronize the movements of the narrow sides of the first support zone with those of the narrow walls of the mold. Furthermore, the narrow sides of the first support zone are not designed to be inclined so that they are unable to conform to the taper of the slab during a width change. For these reasons, it is the practice to back the narrow sides of the first support zone away from the slab while a width change is taking place. This leaves the narrow faces of the slab with no support. The result is a bulging of the narrow faces of the slab caused by the pressure of the molten metal constituting the core of the slab. Bulging is undesirable from a quality standpoint and, in addition, increases the risk of a breakout, i.e., rupture of the skin of the slab and an accompanying escape of the molten metal confined by the skin.
The extent of bulging can be decreased by reducing the casting speed. However, this reduces the output of the continuous casting apparatus.